Tubular systems capable of generating pressure pulses in flowing fluid are sometimes used for communication purposes. In the downhole industry, for example, drilling fluid (or mud) pulse telemetry allows for communication between downhole and surface. Some such systems employ rotary motors that drive ball screws in alternate directions to vary restriction of a valve. The motor must necessarily stop and reverse directions to cause the valve to switch between decreasing and increasing restriction, for example, in the process of generating pressure pulses in the flowing fluid. Although such systems serve the purpose for which they are intended, significant power is expended in overcoming inertia of rotating parts that does not directly contribute to generation of the pressure pulses. Devices and methods that reduce the inefficiencies associated with systems as that described above are always welcome in the field.